The market economics of disc cameras of the type currently on the market dictate the nature of allowable improvements in such cameras. Such cameras are designed for casual use, feature extreme simplicity of operation, and are further intended to provide a finished print of good quality in moderate sizes. The market is highly competitive, with the result that improvements in such cameras must be achieved under a total economy of cost. In particular, such cameras are designed to be unitary in nature i.e. separate accessories such as snap-on or screw in supplemental lenses, separate flash units, etc. are considered to be of dubious marketability; any such changeovers should be accomplished by means of simple mechanical operations carried out by a simple manual or sliding operation of a camera control, with the relevant accessories permanently mounted.
Thus, for example, it is considered desirable that there be provided, within the above mentioned cost limitations, an on-board switchover system to provide for varying the objective lens system between telephoto and relatively wide angle lenses. One proposed approach employed a supplemental lens mounted on a slider, the supplemental lens being slid over the normal objective or picture-taking lens to provide a factor of two increase in magnification. Because of the design constraints on the position and overall optical properties of the main objective lens, it is generally found that slight variations in the position of such a supplemental lens cause a noticeable degradation in image quality, this variation arising from variability of the standoff distance of this supplemental lens because of looseness of the track in which the associated lens mount slides. Moreover, because of basic system constraints, such supplemental lenses are commonly found to be a mediocre substitute for a well-designed unitary objective lens. A related problem is that of providing a viewfinder that will function properly, whichever lens system is in use.
A representative example of the state of the art with respect to disc camera objective lens changeover systems and associated viewfinder changeover systems is found in a conversion system manufactured by Zykkor Manufacturing Co. of Japan, which features a snap-on carrier unit which carries a snap-in supplemental objective lens and a simple opaque framing mask to fit over the viewfinder. Such a system clearly does not fulfill the requirement for a unitary camera.
One possible improvement frequently used in other forms of still cameras is to present continuously, as bright images, a pair of framing rectangles in the viewfinder, the camera operator adjusting the orientation of his camera to place the subject within the appropriate rectangle depending upon which particular lens is currently in use. A frequent source of error arises when the operator fails to note which lens is in place, and hence which set of framing marks should be employed.
Thus, assuming that a practical objective lens changeover system could be developed, there would still be a need for a simple automatically actuated viewfinder changeover system which would uniquely and unambiguously present the proper framing pattern to the operator according to which lens system is currently in position. The fact that the disc camera must be thin as well as inexpensive poses severe restrictions on the forms of systems that may be adopted for this purpose. Too complex a system is unsuitable for such cameras because of the cost-competitive nature of the inexpensive camera market. One approach customarily employed in still cameras, and ruled out by the cost-complexity problem, is that of using an extra viewfinder lens automatically moved into position, as shown, for example, in U.S. Pat. No. 2,653,528 issued to Mueller, which discloses a coupled viewfinder turret lens system slaved to rotation of a turret carrying the objective lenses for a motion picture camera. A similar approach applied to still cameras is disclosed in U.S. Pat. No. 4,104,663 issued to Yamazaki et. al., wherein a supplemental lens is interposed in the optical train of the viewfinder to vary the apparent field thereof.
A further alternative approach is disclosed in U.S. Pat. No. 3,619,202 issued to Bellows, which shows a system for moving boundary-defining vanes slaved to a cam on an objective lens of the zoom type, the vane position varying with the current focal length of setting of the objective. A related and somewhat simpler approach is disclosed in U.S. Pat. No. 3,212,422 issued to Nerwin et. al., showing an extensible set of interlinked springs configured in the form of a rectangle and placed in the field of view, the springs being stretched by strings generally outward from the corners of the rectangle formed therebetween, the strings being slaved to rotation of the barrel of a zoom lens so as to stretch or alternatively relax the size of the rectangular frame so defined. Both of the foregoing examples are quite complex, and if applied to disc cameras would render them prohibitively expensive.
Thus, prior to the present invention, to the applicant's knowledge there has not been provided a simple, inexpensive on-board objective lens changeover system of adequate quality having an associated means for providing a simple viewfinder framing system which automatically adjusts the viewfinder to present the user with an unambiguous field-defining set of framing boundaries for any camera, let alone one which is especially suited for disc cameras.